Early mountaineers used a prussic knot to climb a rope in times of emergency; the classic example being to extricate themselves from a crevasse should they happen to fall in. Prussics were made from small diameter rope which was wrapped around in a certain way- see opposite- to grip the main rope making a hand or foothold. A multitude of mechanical versions have appeared over the decades, many of them catering for the new world of industrial rope access. Mountaineers require something light and less bulky than the industrial versions and many still use prussics with a simple variation called the French Prussic. These Tiblocs are one of the smallest and lightest mechanical versions. The downward pressure created by the karabiner when weighted causes the rope to engage with the ‘teeth’ and grip. A sling can be attached for hand/foot hold which means you should be out of the crevasse and home for tea!